The present invention is directed to a downhole tool, and more particularly to a reamer shoe attachment for a flexible casing guide running tool.
In oil and gas exploration and production operations, bores are drilled to gain access to subsurface hydrocarbon-bearing formations. The bores are typically lined with steel tubing, known as tubing, casing or liner, depending upon diameter, location and function. The tubing is run into the drilled bore from the surface and suspended or secured in the bore by appropriate means, such as a casing or liner hanger. For a casing, cement may then be introduced into the annulus between the tubing and the bore wall.
As the tubing is run into the bore, the tubing end will encounter irregularities and restrictions in the bore wall, for example ledges formed where the bore passes between different formations and areas where the bore diameter decreases due to swelling of the surrounding formation. Further, debris may collect in the bore, particularly in highly deviated or horizontal bores. Accordingly, the tubing end may be subjected to wear and damage as the tubing is lowered into the bore. These difficulties may be alleviated by providing a shoe on the tubing end. Examples of casing shoes of various forms are well known in the art.
Another problem encountered is the difficulty of running casing through build sections. More specifically, there is difficulty in running large diameter casing through the build section of a well in moderate to soft formations. The stiffness of the casing requires a significant force that must be generated at the casing shoe to cause the casing to bend to follow the curved section of the wellbore.
Often times a reamer bit is attached to the bottom of a casing shoe for opening the hole and smoothing areas that may have ledges or under-gauge areas where the diameter of the hole is not large enough to allow passage of the casing. Often, a bit or reamer attached to the casing or liner must itself be able to be drilled. Existing reamer shoes that can be drilled are often made of aluminum, ceramic powder polymer composites, or fiber reinforced composites, with tungsten carbon inserts or grit. The use of metallic carbide, usually tungsten carbide, are in the form of sintered compact inserts, welded hardfacing, or grit that is included in a matrix. Also, polycrystalline diamond (PDC) inserts are sometimes used. The problem with PDC inserts is that they are expensive, and are made by bonding a layer of diamond to tungsten carbide. Tungsten carbide is very hard, abrasive and most importantly has a very high density. This means the reamer will be difficult to drill, and when it is drilled through, the tungsten carbide pieces are going to reside in the bottom of the well and because of their high density precludes them from being flushed out of the hole through normal circulation. In horizontal and directional wells, these pieces can cause wear and damage to other steel downhole components during further drilling operations. Consequently, a need exists for a reamer shoe attachment for a flexible casing shoe that solves the problems of existing reamer shoe designs.